Five years ago, the jobbing actress Deirdre O'Kane took the train to Kilkenny to have a gawk and a giggle at this outlandish notion of an international comedy festival in the marble city. Four laughed-out days later on the way back to Dublin, the actress had become a comedian. The Cat Laughs festival persuaded her to leave the Abbey Theatre and seek out a small, grotty room in a pub. Five years later, she repays her debt to Kilkenny by headlining her own show at this year's festival.

O'Kane's conversion from "the chance to wear nice pretty frocks in interesting roles in front of polite and attentive audiences" to "telling gags in smoky pubs to drunk audiences" was no great act of romantic idealism, though. What struck her most on her first "observer status" trip to Kilkenny was (1) why weren't more women doing stand-up? and (2) how she could have a bit more control over her working life if she could double up a comedian in between waiting to hear back from auditions.

"I suppose, though, what really clinched it," says the 29-year-old Drogheda-raised but Dublin-based comic, "was seeing a certain comic four nights in a row at the festival. He did the same material each night, just like actors do in a play, and I just thought on the way home from the weekend that all I needed to do was write some material and I could do the exact same thing." It wasn't that she wasn't a successful actress - she was, and had just finished a two-year world tour with the Druid production of The Black Pigs Dyke - it was more that she was quickly tiring of "coming second" for important acting jobs. Once she was among the last two for a high-profile, well-paid job on Coronation Street; another time she was cast in a big-budget film, to star alongside Tom Conti and Julie Walters - except the producers went bankrupt soon after she signed the contract. "It wasn't that I left acting, it's just that I put it aside while I set about becoming a comic," she says, "I knew I had the performance skills so what I had to worry about then was writing some original material for myself. I knew I couldn't do what Eddie Izzard does, so I just tried to write some stories that were based, or partly based, on my own experiences."

For a woman who had acted in front of big audiences all around the world, her debut as a comic in front of 50 people in Dublin's Comedy Cellar club was more than a shock to the system. "I was absolutely petrified," she remembers. "Nothing had prepared me for it and I'll never forget how frightened I was. I thought they could hear my heart beating down in O'Connell Street." With the modesty that characterises her approach to her work, she says her first night went "okay" but she couldn't get over the difference between her old job and her new one.

"With acting, there is a certain etiquette there, you get about five weeks in rehearsal before you step on the stage and you don't get people in the audience shouting `fuck off, you're crap' up at you. Also, I think when you write your material and perform it, you're open to way more criticism. Even when the terror subsided slightly, I still hated doing it and for the first two years I just kept getting blinding headaches all the time. The only reason I continued was that I kept getting booked."

She doesn't believe gender is an issue in her new field: "Of course it would be better having more women doing more things and that includes stand-up, but they have to be good at what they're doing also, otherwise there's no point. When I came on the scene, there was The Nualas who were doing character comedy, but there weren't any other women doing stand-up because Michelle Read had gone more into theatre. The only thing that struck me was sometimes when the MC would say `and now for a very funny woman . . . ' you could actually hear a sigh from the audience when he said `woman'. Maybe it's because they thought they were going to hear `tampon talk' for the next 20 minutes but in reality that sort of material died out in the 1980s. What I would say about it is that you have to spend the first five minutes showing the audience that you're funny and you have to overcome that obstacle - and that's one thing that men don't have."

How did your acting colleagues view the switch from doing Chekov to telling gags in pubs? "I'm sure that main thing was `well, that's one more actor out of the way' but actually actors have a lot of respect for comedians, particularly because they recognise comics write their own material. Because I've been so busy as a comic, I haven't done an acting job for a year, and I do miss it sometimes but I suppose this is what I do now."

She says it's only after getting through her first Edinburgh Festival last year that she now feels comfortable as a comedian. "The Fringe is great like that because you're performing for 26 nights in a row to different audiences each night, and that gives you a good sense of discipline. Money couldn't buy the course in comedy that Edinburgh provides and it's only since then that I've think I've really developed as an act."

Asked to describe her material she shrugs her shoulders and says "some people say it's very cynical". In reality, it's a series of narratives, some of which have a sardonic core, some don't. O'Kane, unlike the new wave of the surrealists, grounds her story in real experiences and issues. By no means an observational comic, she does use observations to kick-start a free-flowing story. Even as a comic, though, she can't escape the occupational hazards that occasionally hijacked her old career. At last year's Edinburgh, a production team related to Channel 4 were scouting for new talent and went along to see her show. They were mightily impressed by O'Kane's set and offered her a very big and high-profile job presenting a well known comedy show for Channel 4 - the sort of break most comics would happily kill their families for. She did some pilots, went about finding a flat in London and was busy equipping herself with a new wardrobe for television when she got word that she was been replaced at the very last moment. The contract she signed with Channel 4 precludes her from naming names or talking in detail about the incident. "A similar thing happened to me as an actress and in that case because I was promised the job, I had turned down two theatre jobs - so when the job fell through I was unemployed for six months.

This time, though, even though I was really disappointed at the time, I have so much work going on, from live stand-up gigs to parts in very well-advanced new sitcoms for BBC, that I haven't time to care that much. I'll get there eventually, and on my own terms."

Deirdre O'Kane performs at Cleere's on June 4th (11 p.m.) and The Kilford Arms on the 5th and 6th (10 p.m.)